What is the test of instrumentality in the context of a claim for instrumentality?

I further note the reservation of Lord Walker in OBG where he expressed a view that the relevant issue is not yet closed. He stated at para. 269: Faced with these alternative views I am naturally hesitant. I would respectfully suggest that neither is likely to be the last word on this difficult and important area of the law. The test of instrumentality does not fit happily with cases like RCA Corpn v. Pollard, since there is no doubt that the bootlegger’s acts were the direct cause of the plaintiff’s economic loss. The control mechanism must be found, it seems to me, in the nature of the disruption caused, as between the third party and the claimant, by the defendant’s wrong (and not in the closeness of the casual connection between the defendant’s wrong and the claimant’s loss). [emphasis added]